Extension ready spinal support systems

ABSTRACT

An “extension ready” spinal support system that enables the extension to be accomplished with minimal disturbance to an existing spinal support structure to which the extension system is coupled. In some embodiments, the existing spinal support rod and pedicle screws can remain intact while extension subassemblies are mounted directly to the existing base rod receptacles. The extension subassemblies include a skirt portion that surrounds and engages the existing base receptacle to prevent splaying of the base receptacle. Additional resistance to splaying may be provided by a canted thread arrangement between the skirt and the base receptacle. In some embodiments, the extension receptacle is provided with a low profile (i.e., shortened axial length from the base rod receptacle) by providing a monoaxial rotation structure that rotates about but does not pitch relative to the extension axis and is shorter relative to polyaxial rotation structures.

RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 62/500,820 filed on May 3, 2017, and U.S. ProvisionalPatent Application No. 62/500,719, also filed May 3, 2017, thedisclosures of which are hereby incorporated by reference in theirentirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to spinal support systems and moreparticularly to a spinal support systems and methods that areextensible.

BACKGROUND OF THE DISCLOSURE

Implementation of various spinal surgical techniques often require theuse of spinal support rods that are anchored to the vertebrae throughthe use of pedicle screws to provide stabilization of the spine duringhealing or correction. Examples include maintaining adjacent vertebraestationary so that bone growth tissue can bridge the vertebrae in aspinal fusion process. Another example is the use of spinal support rodsto apply a coercive force to the spine for corrective purposes (e.g.,correction of scoliosis).

In some cases, surgery is later required to treat other vertebrae of thesame patient. “Extension” systems have been developed which enableadditional spinal support rods to be coupled to existing spinal rods orpedicle screws of the previous surgery, thereby reducing surgical traumaand recovery times. Such an extension system is found, for example, atU.S Patent Application Publication No. 2016/0242817 to Abbasi entitled“Spinal Rod Support Structure with Clamp,” owned by the owner of thecurrent application, the contents of which are incorporated by referenceherein except for patent claims and express definitions containedtherein.

The present application identifies shortcomings and limitations in theart of spinal rod extension systems and provides improvements to remedysuch shortcomings and limitations.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure provides an “extensionready” spinal support system that enables the extension to beaccomplished with minimal disturbance to an existing spinal supportstructure to which the extension system is coupled. In some embodiments,existing connections between the existing spinal support rod and pediclescrews can remain intact while extension rod receptacles are mounteddirectly to the existing base rod receptacles. In some embodiments, theextension receptacle may be polyaxial with respect to the basereceptacle. In other embodiments, the extension receptacle is providedwith a low profile (i.e., shortened axial projection length from thebase rod receptacle) relative to the polyaxial embodiment by eliminatingpolyaxial structure between the base receptacle and the extensionreceptacle and the additional axial lengths associated therewith andproviding a monoaxial structure that rotates about but does not pitchrelative to extension axis.

Conventional spinal rod extension systems exist where extension spinalsupport rod receptacles (also referred to as extension “tulips” in theparlance of the spinal support arts) can be mounted “piggyback” to anexisting or “base” spinal support rod receptacle. However, conventionalsystems require that the connection between the base spinal support rodreceptacle must be disturbed or modified. For example, in some systems,the set screw securing the base spinal rod to the base receptacle mustbe removed so that the extension receptacle can utilize the interiorthreads of the base receptacle. This releases the base spinal supportrod from the base receptacle, thus requiring that the base spinalsupport rod be reset before the surgeon can proceed with implantation ofthe extension system. Often, the required structure that extends fromthe base receptacle is of undesirable axial length, causing concealmentissues.

Another drawback of conventional rod receptacle arrangements is theseparation or “splaying” of the tulip. When a conventional set screw isseated on the inside of a conventional tulip, forces are generated onthe tulip wall portions that force the tulip wall sections away fromeach other. This separation of the tulip walls is referred to as“splaying.”

Various embodiments of the disclosure alleviate one or more of theseshortcomings and limitations. The disclosed embodiments enable extensionof the spinal support structure without need for removing the tulips orpedicle screws of the already-implanted spinal support structure.Certain embodiments alleviate the need to remove the set screw from theinterior threads of the base receptacle. As with conventional rodreceptacles, the disclosed base rod receptacle includes interior threadsto which a set screw is coupled for securing the base spinal supportrod. In addition, the disclosed system further includes exterior threadsto which an optional extension assembly can be mounted at a later time.By utilizing the exterior threads for mounting the extension system, theset screw that secures the base spinal support rod to the base rodreceptacle does not have to be removed from the interior threads of thebase rod receptacle. In this way, the base spinal support system canremain intact and undisturbed as the extension system is coupledthereto.

Other embodiments involve removal of the set screw from the basereceptacle, but utilizes a reinforced, dual threaded or capped base thatis stronger and more robust than standard set screw arrangements andprevents splaying of the tulip.

Structurally, a spinal support system is disclosed, comprising a firstrod receptacle for mounting to a pedicle screw, the first rod receptaclehaving a first side wall that includes a first interior surface and afirst exterior surface. The first side wall defines a first pair ofdiametrically opposed slots that extend axially along the first sidewall and are open at a proximal end of the first rod receptacle, thefirst interior surface defining first interior threads. A first setscrew includes threads configured to mate with the first interiorthreads of the first rod receptacle. The first exterior surface definesfirst exterior threads. An extension assembly including a base portionmounted to a second rod receptacle, the base portion including amounting platform and a skirt portion that extends from the mountingplatform, the skirt portion including interior threads for mating withthe first exterior threads of the first rod receptacle, the second rodreceptacle having a second side wall that includes a second interiorsurface and a second exterior surface. The second exterior surface ofthe second rod receptacle may include second exterior threads. Thesecond side wall defines a second pair of diametrically opposed slotsthat extend axially along the second side wall and are open at aproximal end of the second rod receptacle, the second interior surfacedefining second interior threads. A second set screw includes threadsconfigured to mate with the second interior threads of the second rodreceptacle.

The extension assembly may include a pivot member that attaches thesecond rod receptacle to the base portion, the pivot member including ahead portion and a shaft portion, the shaft portion including shaftthreads formed on an exterior surface thereof, the shaft portiondefining a pivot axis. In some embodiments, the second rod receptacledefines an opening at a distal end thereof, the opening sized toaccommodate passage of the shaft portion of the pivot member. Themounting platform of the base portion may define a center hole forreceiving the pivot member, and may include interior threads for matingwith the external shaft threads. In some embodiments, the center hole isa through hole.

In some embodiments, the second rod receptacle includes an internalflange having an interior face, the head portion of the pivot memberbeing dimensioned to register against the interior face of the internalflange to secure the second rod receptacle to the base portion. The headportion of the pivot member may be one of a flat head and a countersinkhead, and the interior face of the internal flange of the second rodreceptacle may conforms to the head portion to enable selectivemonoaxial rotation about the pivot axis.

In some embodiments, a pedicle screw coupled to a distal end portion ofthe first rod receptacle. The pedicle screw and the first rod receptaclemay be configured for polyaxial rotation of the first rod receptacleabout a head of the pedicle screw. In some embodiments, a lock ringconfigured to engage a spinal support rod, the lock ring including adistal face that conforms to the pedicle screw and a proximal face thatincludes one or more malleable features for engaging the spinal supportrod. The one or more malleable features may be plastically deformable.In some embodiments, the one or more malleable features includes araised ridge. In some embodiments, the raised ridge is annular ring.

Some embodiments include a cap including a skirt portion having interiorthreads for mating with the second exterior threads of the second rodreceptacle. In some embodiments, the skirt is not threaded, but insteadprovides a sliding fit over the exterior of the base rod receptacle toprevent splaying. An exterior surface of the skirt portion may define aplurality of flats, each of said plurality of flats being parallel tothe pivot axis. In some embodiments, one or more of the first interiorthreads, the first exterior threads, the second interior threads, thesecond exterior threads, and the internal threads of the center holedefine a canted cantilever profile. The canted cantilever profile mayextend radially and in a distal direction.

In various embodiments of the disclosure, a spinal rod support systemcomprises an extension rod receptacle, a base portion including amounting platform that defines a center hole accessible from a proximalface of the mounting platform, and means for coupling the extension rodreceptacle to the base portion. In some embodiments, the means forcoupling the extension rod receptacle to the base portion includes apivot member threadably engaged with the center hole. In someembodiments, the means for coupling the extension rod receptacle to thebase portion includes a pivot member swaged to the center hole. In someembodiments, the means for coupling the extension rod receptacle to thebase portion includes a pivot member fused to the center hole. The pivotmember may be welded to the center hole at a distal face of the baseportion, for example, a distal face of the mounting platform.

The spinal support system may further comprise a base rod receptacle,and means for coupling the base portion to the base rod receptacle. Insome embodiments, the base portion includes a skirt portion, and themeans for coupling the base portion to the base rod receptacle includesthreaded engagement of the skirt portion to the base rod receptacle. Insome embodiments, the base portion includes a set screw portion that isunitary with and extends from a distal face of the mounting platform,and the means for coupling the base portion to the base rod receptacleincludes threaded engagement of the set screw portion to the base rodreceptacle. In some embodiments, the set screw portion and the baseportion include mating threads that define canted cantilever profilesfor the threaded engagement. The canted cantilever profiles may extendradially and in a distal direction. In some embodiments, the spinalsupport system comprises a base spinal support rod disposed in the baserod receptacle, the set screw portion being configured to clamp the basespinal support rod within the base rod receptacle. In some embodiments,the base portion includes a set screw portion that is unitary with andextends from a distal face of the mounting platform, and the means forcoupling the base portion to the base rod receptacle includes threadedengagement of the set screw portion to the base rod receptacle. In someembodiments, the means for coupling the extension rod receptacle to thebase portion enables only monoaxial rotation of the extension rodreceptacle about a pivot axis.

In various embodiments of the disclosure, a method of fabricating anextension assembly for a spinal support system comprises: inserting apivot member into a rod receptacle so that a shaft portion of the pivotmember extends from a distal end of the rod receptacle; disposing theshaft portion in a center hole of a base portion so that an internalflange of the rod receptacle is captured between a head portion of thepivot member and the base portion so that an axial gap dimension definedbetween the head portion and the base member is greater than an axialthickness of the internal flange; and securing the pivot member to thebase portion. In some embodiments, the step of disposing and the step ofsecuring includes threadably engaging the shaft portion with the centerhole. In some embodiments, the step of disposing includes registering astop on the pivot member against the base portion to define the axialgap dimension. In some embodiments, the step of securing includes one offusing and swaging the shaft member to the base portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an extension ready base assemblyaccording to an embodiment of the disclosure;

FIG. 1A is an upper perspective view of a base rod receptacle of FIG. 1in isolation according to an embodiment of the disclosure;

FIG. 2 is a sectional view of an extensible spinal support system infull assembly with the extension ready base assembly of FIG. 1 accordingan embodiment of the disclosure;

FIG. 3 is an enlarged, partial sectional view of a lock ring in theassembly of FIG. 2 according to an embodiment of the disclosure;

FIG. 4 is an enlarged, partial sectional view of a threaded wall portionof a base rod receptacle of the assembly of FIG. 2 according to anembodiment of the disclosure;

FIG. 5 is an enlarged, partial sectional view of a threaded wall portionof an extension rod receptacle of the assembly of FIG. 2 according to anembodiment of the disclosure;

FIGS. 6 through 8 are sectional views of alternative extensible spinalsupport systems in full assembly with the extension ready base assemblyof FIG. 1 according embodiments of the disclosure;

FIG. 9 is a perspective view of a platform of an extensible spinalsupport system with exterior wrench flats according to an embodiment ofthe disclosure;

FIGS. 10 and 11 are sectional views depicting assembly of an extensionsub-assembly having a threaded pivot member according to an embodimentof the disclosure;

FIGS. 12 and 13 are sectional views depicting assembly of an extensionsub-assembly having a welded pivot member according to an embodiment ofthe disclosure;

FIGS. 14 and 15 are sectional views depicting assembly of an extensionsub-assembly having a riveted pivot member according to an embodiment ofthe disclosure;

FIGS. 16 and 17 are sectional views of extension sub-assemblies withbase portions that have integral set screw portions according to anembodiment of the disclosure;

FIG. 18 is a perspective view of the pedicle screw of FIGS. 1 and 2according to an embodiment of the disclosure;

FIG. 19 is a top axial view of the pedicle screw of FIG. 18 according toan embodiment of the disclosure;

FIG. 20 is a sectional view of the pedicle screw at plane XX-XX of FIG.18 according to an embodiment of the disclosure;

FIG. 21 is a top axial view of a set screw according to an embodiment ofthe disclosure;

FIG. 22 is a section view of the set screw XXII-XXII of FIG. 21 at planeaccording to an embodiment of the disclosure;

FIG. 23 is a perspective view of the set screw of FIG. 21 according toan embodiment of the disclosure;

FIG. 24 is a perspective view of a lock ring according to an embodimentof the disclosure;

FIG. 25 is a sectional view of a conventional rod receptacle inassembly;

FIG. 25A is an enlarged, partial view of FIG. 25;

FIG. 26 is a sectional view of a rod receptacle in assembly havingthreads that define canted cantilever profile according to an embodimentof the disclosure; and

FIG. 26A is an enlarged, partial view of FIG. 26 according to anembodiment of the disclosure.

DETAILED DESCRIPTION OF THE FIGURES

Referring to FIGS. 1 through 5, an extensible spinal support system 20is depicted according to an embodiment of the disclosure. The extensiblespinal support system 20 as depicted includes an extension ready baseassembly 21 including a pedicle screw 22, a first or base rod receptacle24, a first or base set screw 42, and a first spinal support rod 36(FIG. 1). The extensible spinal support system 20 further includes anextension subassembly 26 and a cap 28 (FIG. 2). The extensionsubassembly 26 includes a base portion 32 and a second or extension rodreceptacle 34. The base rod receptacle 24 is configured to receive thefirst or base spinal support rod 36, and the extension rod receptacle 34is configured to receive a second or extension spinal support rod 38. Inthe depicted embodiments, the base spinal support rod 36 is retainedwithin the base rod receptacle 24 with the base set screw 42. Likewise,for the extensible spinal support system 20, the extension spinalsupport rod 38 is retained within the extension rod receptacle 34 with asecond or extension set screw 44.

The pedicle screw 22 includes a head portion 64 and a threaded shaftportion 65 centered about a central axis 67. The pedicle screw 22extends from a distal end 62 of the base rod receptacle 24, the headportion 64 being captured within the distal end 62 of the base rodreceptacle 24. In some embodiments, a lock ring 66 is disposedinterstitially between the base spinal support rod 36 and the headportion 64 of the pedicle screw 22. In the depicted embodiment, the headportion 64 of the pedicle screw 22 defines a spherical surface portion68, with the base rod receptacle 24 including a complementary matingsurface 72 that engages and conforms to the spherical surface portion 68of the head portion 64 of the pedicle screw 22.

Functionally, the spherical surface portion 68 of the head portion 64 ofthe pedicle screw 22 and conforming mating surface 72 of the base rodreceptacle 24 enable the base rod receptacle 24 to pitch about the headportion 64 of the pedicle screw 22 relative to the central axis 67, andto rotate about the head portion 64 in any of the pitched orientations.By this arrangement, the pedicle screw 22 and the base rod receptacle 24are configured for polyaxial rotation of the base rod receptacle 24about the head portion 64 of the pedicle screw 22.

Herein, “proximal” refers to a direction 76 that is toward a surgeonduring operation or implantation and away from a bone or patient.“Distal” refers to a direction 74 that is away from the surgeon duringoperation or implantation and toward the bone or patient to which theextensible spinal support system 20 is implanted (i.e., a directionopposite the distal direction 76).

The base rod receptacle 24 includes a side wall 82 having an interiorsurface 84 and an exterior surface 86. A pair of diametrically opposeslots 88 are defined on the side wall 82, the slots 88 extending axiallyalong the side wall 82 and being open at a proximal end 92 of the baserod receptacle 24. By formation of the diametrically opposed slots 88,the side wall 82 defines diametrically opposed wall segments 90 onopposing sides of the diametrically opposed slots 88. The interiorsurface 84 extends axially along the side wall 82 and includes interiorthreads 94 formed thereon. The exterior surface 86 also extends axiallyand includes exterior threads 96 formed thereon. The base portion 32 ofthe extension subassembly 26 includes a mounting platform 122 and askirt portion 124 that extends from the mounting platform 122 in thedistal direction 74. The skirt portion 124 includes an interior surface123 and an exterior surface 125.

The extension rod receptacle 34 includes a side wall 142 having aninterior surface 144 and an exterior surface 146. A pair ofdiametrically opposed slots 148 are defined on the side wall 142, theslots 148 extending axially along the side wall 142 and being open at aproximal end 152 of the extension rod receptacle 34. By formation of thediametrically opposed slots 148, the side wall 142 defines diametricallyopposed wall segments 150 on opposing sides of the diametrically opposedslots 148. The interior surface 144 extends axially along the side wall142 and includes interior threads 154 formed thereon (FIG. 5). Theexterior surface 146 also extends axially and includes exterior threads156 formed thereon.

In the depicted embodiment, the extension subassembly 26 includes apivot member 170 that attaches the extension rod receptacle 34 to thebase portion 32, the pivot member 170 including a head portion 172 and ashaft portion 174 and defining a through passage 175. The shaft portiondefines a pivot axis 182. The extension rod receptacle 34 defines anopening 184 at a distal end 186 thereof. The opening 184 is sized toaccommodate passage of the shaft portion 174 of the pivot member 170.

In the depicted embodiment, the mounting platform 122 of the baseportion 32 defines a center hole 188 for receiving the pivot member 170.The extension rod receptacle 34 may include an internal flange 194having an interior face 196, the head portion 172 of the pivot member170 being dimensioned to extend radially over the interior face 196 ofthe internal flange 194 to loosely secure the extension rod receptacle34 to the base portion 32. The head portion 172 of the pivot member 170may be one of several head styles available to the artisan, for examplea flat head (depicted), a socket head, a countersink head, or aspherical head. The interior face 196 of the internal flange 194 may beconfigured to conform to the head portion 172. In some embodiments, acollet 198 is disposed interstitially between the extension spinalsupport rod 38 and the head portion 172. The collet 198 may be a discspring (depicted), lock washer, or other that exerts a bias forceparallel to the pivot axis 182 when compressed between the support rod38 and the head portion 172. The cap 28 includes a top portion 222 and askirt portion 224 that extends from the mounting platform 222. The skirtportion 224 includes interior threads 226 for mating with the exteriorthreads 156 of the extension rod receptacle 34.

In operation, the pedicle screw 22 is inserted into the base rodreceptacle 24 so that the head portion 64 of the pedicle screw 22 can beregistered against the mating surface 72 of the base rod receptacle 24.The pedicle screw 22 is set into the bone of a vertebrae. The lock ring66, if utilized, is disposed within the base rod receptacle 24 andarranged for contact with the head portion 64 of the pedicle screw 22.The base rod receptacle 24 is arranged in a desired orientation on thehead portion 64 of the pedicle screw 22 and the base spinal support rod36 disposed in the base rod receptacle 24. The lock ring 66 is therebydisposed between the base spinal support rod 36 and the head portion 64of the pedicle screw 22. The base set screw 42 is threadably engagedwith the interior threads 94 of the side wall 82 and tightened so thatthe base spinal support rod 36 is clamped between the base set screw 42and the lock ring 66 (if utilized) or, alternatively, the head portion64 of the pedicle screw 22. The tightening of the base set screw 42 alsoseats the head portion 64 of the pedicle screw 22 against the matingsurface 72 of the base rod receptacle 24 to secure the base rodreceptacle 24 in the desired orientation relative to the head portion64.

Referring to FIGS. 6 and 7 and again to FIG. 2, extensible spinalsupport systems 20 having alternative embodiments for the base portion32 are presented according to embodiments of the disclosure. In FIGS. 2,6, and 7, the extensible spinal support systems and their associatedbase portions are referred to collectively and generically by referencecharacters 20 and 32, respectively, and specifically by the referencecharacters 20 and 32 followed by a letter suffix (e.g., extensiblespinal support system 20 a and the associated base portion 32 a).Several components and attributes are common to all extensible spinalsupport systems 20, which are indicated with same numbered referencecharacters.

For the extensible spinal support system 20 a (FIG. 2), the base portion32 a and the base set screw 42 are separate components that areinstalled independently of each other. For the extensible spinal supportsystems 20 a and 20 b, the skirt portion 124 includes interior threads126 for mating with the exterior threads 96 of the base rod receptacle24. For the extensible support system 20 b (FIG. 6), the base portion 32b additionally includes a set screw portion 228 that is integraltherewith, the set screw portion 228 having external threads 232 thatmate with the interior threads 94 of the side wall 82 of the base rodreceptacle 24. Accordingly, for the extensible spinal support system 20b, the external threads 232 of the set screw portion 228 and theinterior threads 226 of the skirt portion 124 of the base portion 32 bare threaded simultaneously. For the extensible spinal support system 20c (FIG. 7), the base portion 32 c also includes the set screw portion228 that is integral therewith, and having external threads 232 thatmate with the interior threads 94 of the side wall 82 of the base rodreceptacle 24. However, for the extensible spinal support system 20 c,an inner surface 234 the skirt portion 124 is smooth (does not includeinterior threads), such that the skirt portion 124 rotates about andslides over but does not threadably engage the exterior threads 96 ofthe base rod receptacle 24. Accordingly, the base portion 32 c matesonly with the interior threads 94 of the side wall 82.

By integrating the set screw portion 228 with the mounting platform 122as in subassemblies 26 b and 26 c, and skirt portion 124 the structuralintegrity of the extensible spinal support system 20 is enhanced. Forexample, lateral forces applied to the extensible spinal support system20 will incur greater resistance because the integrated set screwportion 228 is unitary with the mounting platform 122, establishing ashear stress at the junction of the integrated set screw portion 228 andthe mounting platform 122 that provides additional resistance todeformation relative to the extension subassemblies 26 of FIGS. 10through 15.

Functionally, each of the extensible support systems 20 provide a uniqueadvantage. Extensible spinal support system 20 a enables mounting of theextension assembly 26 without disturbing the base set screw 42,eliminating the need to reset the base spinal support rod 36. Theextensible spinal support system 20 a may find application wheredisturbance of the base spinal support system is not necessary or is illadvised. Extensible spinal support system 20 b provides a dual threadedarrangement that enhances structural integrity of the extension assembly26 to the base rod receptacle 24. Such enhancement of the structuralintegrity may be advantageous for high torque and high stressapplications, such as scoliosis correction. Extensible spinal supportsystem 20 c also includes the integrated set screw portion 228 andattendant benefit while the smooth, sliding fit of the skirt portion 124enables easier installation where the dual threaded arrangement of theextensible spinal support system 20 b may be unnecessary or difficult.The sliding fit of the skirt portion 124 for the extensible spinalsupport system 20 c effectively captures the side walls 82 of the baserod receptacle 24 to limit splaying. The extensible spinal supportsystem 20 c can also be configured for retrofitting with tulips of otherspinal support systems that are not extension ready.

Referring to FIG. 8, an extensible spinal support system 20 d isdepicted according to an embodiment of the disclosure. As depicted theextensible spinal support system 20 d includes many of the samecomponents and attributes as the extensible spinal support system 20 a,which are indicated with same numbered referenced characters. Whilecomponents and attributes of the extensible spinal support system 20 aare presented in the extensible spinal support system 20 d, suchcomponents and attributes are not limiting. That is, the extensiblespinal support system 20 d may implement various aspects of theextensible spinal support systems 20 b and 20 c as well.

For the extensible spinal support system 20 d, the head portion 172 ofthe pivot member 170 d is spherical, and the extension rod receptacle 34is configured as discussed above for the base rod receptacle 24. By thisarrangement, the pivot member 170 and the extension rod receptacle 34are configured for polyaxial rotation of the extension rod receptacle 34about the head portion 172 of the pivot member 170.

Referring to FIG. 9, the skirt portion 124 of the base portion 34 isdepicted with flats 240 according to an embodiment of the disclosure.The flats 240 are parallel to the pivot axis 182 and may be implementedwith any of the depicted or contemplated embodiments. The embodiment ofFIG. 9 depicts a total of six flats 240 as a non-limiting example. Insome embodiments the number of flats 240 is in a range of six to twelveinclusive. In some embodiments, the skirt portion 124 defines two flats240 that are diametrically opposed. In some embodiments, the skirtportion 124 defines four flats 240 that are distributed as twodiametrically opposed pairs that are rotationally offset at 90 degreeswith respect to each other.

Referring to FIGS. 10 through 17, assembly of various extensionsubassemblies 26 are depicted according to embodiments of thedisclosure. In FIGS. 10 through 17, the extension subassemblies andtheir associated pivot members are referred to collectively andgenerically by reference characters 26 and 170, respectively, andspecifically by the reference characters 26 and 170 followed by a lettersuffix (e.g., extension subassembly 26 a and the associated pivot member170 a). Several components and attributes are common to all extensionsubassemblies 26, which are indicated with same numbered referencecharacters.

For the extension subassembly 26 a (FIGS. 10 and 11), the pivot member170 a defines exterior shaft threads 176 formed on an exterior surface178 of the shaft portion 174. The center hole 188 of the mountingplatform 122 includes internal threads 192 for mating with the exteriorshaft threads 176. In some embodiments, the pivot member 170 a includesa stop 242, such as a shoulder 244 having a diameter 246 that is greaterthan the diameter of the exterior shaft threads 176. The stop 242cooperates with the head portion 172 to define an axial gap dimension248 that is greater than an axial thickness 250 of the internal flange194.

In assembly, the pivot member 170 a is inserted through the extensionrod receptacle 34 and into the opening 184 so that the shaft portion 174extends from the distal end 186 of the extension rod receptacle 34 andthe head portion 172 of the pivot member 170 a is within the extensionrod receptacle 34. The shaft portion 174 of the pivot member 170 a andthe center hole 188 of the mounting platform 122 of the base portion 32a are then aligned and the exterior shaft threads 176 of the shaftportion 174 threaded into the internal threads 192 of the center hole188. In some embodiments, the pivot member 170 a is threaded into thecenter hole 188 until the stop 242 is firmly seated against the platform122 over the mouth of the center hole 188 to define the axial gapdimension 248. Alternatively, the pivot member 170 a may otherwiseengage the base portion 32 a in a manner that causes the pivot member170 a to stop within the center hole 188; for example, the threads 176may cease at a point on the pivot shaft 174 that provides the desiredaxial gap dimension 248. Having secured the pivot member 170 a to themounting platform 122, the extension rod receptacle 34 is coupled to thebase portion 32.

For the extension subassembly 26 b (FIGS. 12 and 13), the shaft portion174 of the pivot member 170 b is a right cylinder 252, defining a smoothexterior surface 178. The center hole 188 of the mounting platform 122is also right cylindrical, and may be dimensioned to provide a closesliding fit with the shaft portion 174. In some embodiments, the pivotmember 170 a includes a stop (not depicted) akin to pivot member 170 a.

In assembly, the pivot member 170 b is inserted through the extensionrod receptacle 34 and into the opening 184 so that the shaft portion 174extends from the distal end 186 of the extension rod receptacle 34 andthe head portion 172 of the pivot member 170 b is within the extensionrod receptacle 34. The shaft portion 174 of the pivot member 170 b andthe center hole 188 of the mounting platform 122 of the base portion 32are then aligned and the shaft portion 174 positioned within the centerhole 188 to so that the axial gap dimension 248 is defined between thehead portion 172 and the mounting platform 122. In some embodiments, thepivot member 170 a is threaded into the center hole 188 until the stop242 is firmly seated against the platform 122 over the mouth of thecenter hole 188, thereby defining the axial gap dimension 248. In someembodiments, the length of the shaft portion 174 is dimensioned toprovide the desired axial gap dimension 248 when a distal end 253 of theshaft portion 174 is flush with a distal face 256 of the platform 122.

With the pivot member 170 b positioned in the center hole 188 to definethe axial gap dimension 248 greater than the axial thickness 250 of theinternal flange 194, the pivot member 170 b is secured to the platform122. In the depicted embodiment, the distal end 253 of the pivot member170 b is welded to the distal face 256 of the mounting platform 122 toform a weld 254 at the perimeter of the center hole 188. The weld 254may be continuous, a stitch weld, or a tack weld. The welding operationmay be performed with welding techniques available to the artisan,including but not limited to electron beam welding. Alternatively,instead of welding, the pivot member 170 b may be secured by otherbonding or fusion techniques, such as brazing, soldering, or gluing.Upon securing the pivot member 170 b to the base portion 32, theinternal flange 294 of the extension rod receptacle 34, being capturedbetween the head portion 172 and the mounting platform 122, is coupledto the base portion 32.

For the extension subassembly 26 c (FIGS. 12 and 13), the shaft portion174 of the pivot member 170 c is also the right cylinder 252, definingthe smooth exterior surface 178. The center hole 188 of the mountingplatform 122 is also right cylindrical, and may be dimensioned toprovide a close sliding fit with the shaft portion 174. Similar to thepivot member 170 a, the pivot member 170 c may include the stop 242 suchas the shoulder 244 with diameter 246, the diameter 246 being greaterthan the diameter of the center hole 188. As with the subassembly 26 a,the stop 242 of the subassembly 26 c cooperates with the head portion172 to define an axial gap dimension 248 that is greater than an axialthickness 250 of the internal flange 194. The distal face 256 of themounting platform 122 may define a recessed lead in 258 that surroundsthe center hole 188.

In assembly, the pivot member 170 c is inserted through the extensionrod receptacle 34 and into the opening 184 so that the shaft portion 174extends from the distal end 186 of the extension rod receptacle 34 andthe head portion 172 of the pivot member 170 c is within the extensionrod receptacle 34. The shaft portion 174 of the pivot member 170 c andthe center hole 188 of the mounting platform 122 of the base portion 32are then aligned and the shaft portion 174 positioned within the centerhole 188 so that the axial gap dimension 248 is defined between the headportion 172 and the mounting platform 122. In some embodiments, thepivot member 170 c is inserted into the center hole 188 until the stop242 registers against the platform 122 over the mouth of the center hole188, thereby defining the axial gap dimension 248. In some embodiments,the length of the shaft portion 174 is dimensioned to provide thedesired axial gap dimension 248 when the distal end 253 is flush withthe distal face 256 of the platform 122.

With the pivot member 170 c positioned in the center hole 188 to definethe axial gap dimension 248 greater than the axial thickness 250 of theinternal flange 194, the pivot member 170 c is secured to the platform122 by a swaging process. The swaging process deforms the distal end 253of the shaft portion 174 into the recessed lead in 258. In this way, themounting platform 122 is swaged between the stop 242 and the deformeddistal end 253 of the pivot member 170 c, akin to a rivet. The internalflange 294 is captured between the head portion 172 of the pivot member170 c and the mounting platform 122 of the base portion 32, therebycoupling the extension rod receptacle 34 to the base portion 32.

The depictions of FIGS. 10 through 15 present base portions 32 akin tobase portion 32 a, i.e., without an integral set screw portion. However,the assembly techniques for the subassemblies 26 described above arereadily implemented for base portions 32 that include the set screwportion 228 integral therewith, akin to base portions 32 b and 32 c. Theembodiments of FIGS. 6 and 7 depict the threaded pivot member 170 a incombination with the integral set screw portion 228. The embodiments ofFIGS. 16 and 17 depict the pivot members 170 b and 170 c with longershaft portions 174 having distal ends 253 that reach the distal faces257 of the integral set screw portions 228. The weld 254 (FIG. 16) andthe recessed lead in 258 (FIG. 17) are formed on the distal faces 257 ofthe integral set screw portion 228. Accordingly, the subassemblies 26may be fabricated with any of the base portions 32 described anddepicted herein.

For the various subassemblies 26, because the axial gap dimension 248 isgreater than the axial thickness 250 of the internal flange 194,monoaxial rotation of the extension rod receptacle 34 about the pivotaxis 182 is achieved. That is, the internal flange 194, thougheffectively captured between the head portion 172 of the pivot member170 and the base portion 32 of the extension subassembly 26, can berotated about the pivot axis 182. In the depicted embodiment, movementof the of the extension rod receptacle 34 relative to the base portion32 is effectively limited to rotation about the pivot axis 182, i.e., a“monoaxial” rotation.

For the subassemblies 26 a and 26 b, because of the exterior threads 96on the side wall 82 of the base rod receptacle 24, the extension rodreceptacle 34 can be mounted to the base rod receptacle 24. That is, theextension subassemblies 26 a and 26 b can be mounted directly to theexterior threads 96 of the base rod receptacle 24. For the subassembly26 c, the extension rod receptacle 24 can be mounted to the interiorthreads of the base rod receptacle 24, without need for exterior threadson the sidewall 82. Accordingly, because of the subassemblies 26, thebase rod receptacle 24 is referred to as “extension ready.”

For the pre-assembled extension subassembly 26 a, the base portion 32 isaligned with the base rod receptacle 24 and the interior threads 126 ofthe skirt portion 124 of the base portion 32 threaded over the exteriorthreads 96 of the base rod receptacle 24. For the pre-assembledextension subassembly 26 b, the base portion 32 is aligned with the baserod receptacle 24 and both the interior threads 126 of the skirt portion124 and the exterior threads external threads 232 of the set screwportion 228 are threadably engage with the exterior threads 96 of thebase rod receptacle 24 and the internal threads 192 of the center hole188, respectively. Because the pivot member 170 is in fixed relationshipwith the base portion 32, the base portion 32 may be drawn tight againstthe proximal end 92 of the base rod receptacle 24 by with a driverinserted in the socket of the pivot member 170. For monoaxialembodiments, the extension rod receptacle 34 may be rotated to a desiredangular orientation about the pivot axis 182. The extension spinalsupport rod 38 is inserted into the extension rod receptacle 34,extending laterally through the diametrically opposed slots 148. Theextension set screw 44 or, alternatively, the set screw portion 228, isthreadably engaged with the interior threads 154 of the side wall 142and tightened. When the set screw 44 is tightened against the extensionspinal support rod 38, the extension rod receptacle 34 is drawn in theproximal direction (upward in FIG. 2) so that the internal flange 194 isdrawn tight against the head portion 172, thereby locking the extensionrod receptacle 34 in place and in a fixed rotational orientationrelative to the head portion 172.

In some embodiments, in the absence of the extension subassembly 26, thecap 28 can be mounted to the exterior threads 96 of the base rodreceptacle 24. Functionally, this arrangement provides support againstoutward lateral deflections (splaying) of the wall segments 90 wouldotherwise be provided by the skirt portion 124 of the mounting platform122 of the extension subassembly 26 a. Other caps can be implementedwith either the base rod receptacle 24 or the extension rod receptacle34, such as disclosed at U.S. patent application Ser. No. 15/970,429,entitled “Reinforcement Caps for Spinal Support Systems”, filed on evendate and owned by the owner of the present application, the disclosureof which is hereby incorporated by reference herein.

Similar to the extensible spinal support system 20 a of FIG. 2, theextensible spinal support systems 20 b and 20 c of FIGS. 6 and 7 may bemounted to a previously implanted extension ready base assembly withoutneed for removing or otherwise releasing the base spinal support rod 36.The base portions 32 b and 32 c of the extension subassemblies 26 b and26 c may be mounted to the extension ready base assembly 21 of FIG. 1instead of the set screw 42, the base portions 32 b and 32 c serving asa cap for securing the base spinal rod 36 to the base rod receptacle 24.The extension rod receptacle 34 can later be mounted directly to thecenter hole 188 of the mounting platform 122 of the base portion 32 bwith the pivot member 170 a, thereby leaving the arrangement of the baserod receptacle 24 the base portions 32 b, 32 c and the base spinalsupport rod 36 intact. Accordingly, the base rod receptacle 24 incombination with the base portions 32 b or 32 c is also referred to as“extension ready.” In such an embodiment, the extension subassemblies 26b and 26 c are not pre-assembled, but instead assembled on the existingbase portion 32 b, 32 c, being built up from the mounting platform 122as described above.

Referring to FIGS. 18 through 20, the pedicle screw 22 is depicted inisolation in an embodiment of the disclosure. In addition to thecomponents and attributes discussed above, the pedicle screw 22 maydefine a socket 262 in the head portion 64, accessible from a proximalend 264 of the pedicle screw 22. The threaded shaft portion 65 may bedouble threaded as depicted. In some embodiments, a center passage 266extends through the head portion 64 and threaded shaft portion 65. Inthe depicted embodiment, the socket 262 is hexagonal, but othergeometries, such as a square, rectangle, cross, or star pattern may beutilized.

Functionally, the socket 262 accommodates driving of the pedicle screw22 with an appropriate mating wrench (e.g., hexagonal wrench for thedepicted embodiment, or a square bit, rectangular bit, cross (PHILLIPS)bit, or star (TORR®) bit as appropriate). The center passage 266 may besized, for example, to accommodate sliding passage of a Kirschner wireor a larger diameter rod.

Referring to FIGS. 21 through 23, the base or extension set screw 42, 44is depicted in isolation in an embodiment of the disclosure. In thedepicted embodiments, the base and extension set screws 42 and 44 areidentical and are referred to collectively and generically as the “setscrew 42, 44”. The set screw 42, 44 includes exterior threads 268 thatmate with the interior threads 94, 154 of the base or extension rodreceptacle 24, 34. The set screw 42, 44 may define a socket 272,accessible from a proximal end 274 of the set screw 42, 44. In someembodiments, a center passage 276 extends from the socket 272 through adistal end 278 of the set screw 42, 44. In the depicted embodiment, thesocket 272 is hexagonal, but other geometries, such as a square,rectangle, cross, or star pattern may be utilized.

Functionally, the socket 272 accommodates driving of the set screw 42,44 with an appropriate mating wrench (e.g., hexagonal wrench for thedepicted embodiment, or a square bit, rectangular bit, cross (PHILLIPS)bit, or star (TORR®) bit as appropriate). The center passage 276 may besized, for example, to accommodate sliding passage of a Kirschner wireor larger diameter rod.

Referring to FIG. 24, the lock ring 66 is depicted in an embodiment ofthe disclosure. In some embodiments, the lock ring 66 includes a distalface 282 and a proximal face 284 separated by a perimeter portion 286.The distal face 282 may be convex and define a spherical profile 288.The proximal face 284 may include one or more malleable features 292 forengaging the base spinal support rod 36. The distal face 282 terminatesat a distal edge 294 of the perimeter portion 286. In the depictedembodiment, a plurality of relief slots 296 are defined that are open atthe distal edge 294 and extend axially into the perimeter portion 286.In some embodiments, the one or more malleable features 292 areplastically deformable. The one or more malleable features 292 maydefine a raised ridge 298, for example an annular ring as depicted inFIG. 24. In some embodiments, the lock ring 66 includes a radial detent299 that extends radially outward from the perimeter portion 286.

Functionally, the convexity of the distal face 282 that accommodates andcan slide over the spherical profile of the head portion 64 of thepedicle screw 22, thereby enabling the polyaxial movement of the baserod receptacle 24 relative to the head portion 64. The one or moremalleable features 292 conform to the shape of the base spinal supportrod 36 when the set screw 42 is tightened to secure the base spinalsupport rod 36 in place. The conformance of the malleable feature(s) 292acts to grip the base spinal support rod 36, thereby inhibiting the basesupport rod 36 from rotating or sliding within the diametrically opposedslots 88 of the base rod receptacle 24. Upon tightening of the base setscrew 42, the relief slots 296 enable the perimeter portion 286 toconform to the head portion 64 at the distal edge 294 for more effectivegripping of the head portion 64 of the pedicle screw 22. The conformanceof the malleable feature(s) 292 and perimeter portion 286 act to secureand inhibit movement between the head portion 64, the base spinalsupport rod 36, and the base rod receptacle 24. The radial detent 299may interface with internal features 297 (FIG. 3) within the base rodreceptacle 24, such as an internal inset flange (depicted) or optionallya groove (not depicted). The internal features 297 restrains theproximal face 284 from deflecting proximally (upward in FIGS. 2 and 3)when the lock ring 66 is deformed under the clamping force between thebase spinal support rod 36 and the head portion 64, thereby maintaininggripping contact between the head portion 64 and the proximal face 284of the lock ring 66.

Referring to FIGS. 25, 25A, 26, and 26A, threads defining a cantedcantilever profile 450 and the advantage provided over conventionalthreaded arrangements are depicted and described according toembodiments of the disclosure. A conventional threaded arrangements 400,schematically depicted at FIGS. 25 and 25A, may include, for example,exterior threads 402 of a set screw 404 that are engaged with interiorthreads 406 of a wall segment 408 of a spinal rod receptacle 410 (akinto opposed wall segments 90 and 150 of the rod receptacles 24 and 34 ofthe extensible spinal support system 20). Both the set screw 404 and thewall segment 408 are concentric about a central axis 412 that definesthe z-axis of a right-cylindrical coordinate system 424 having an axialcoordinate z and a radial coordinate r. When the set screw 404 istightened a first direction 416 to set against a spinal support rod 415,a clamping force vector FC is generated, for which there is an equal andopposite force vector FC′ in a second direction 418 that is opposite thefirst direction 416. The force vector FC′ in turn generates reactionforce vectors FR generated at contact interfaces 422 between theexterior threads 402 of the set screw 404 and the interior threads 406of the wall segment 408. The reaction forces FR generate an axialcomponent FRZ and radial component FRR. Because of the standard shape ofthe threads 402 and 406, the radial components FRR generate a radialoutward force FRO, i.e., away from the central axis 412.

For configurations such as the depicted extensible spinal support system20, the wall segment 408 (e.g., wall segment 90 of the extensible spinalsupport system 20) is, in some embodiments, not supported by anystructure. In such embodiments, the wall segment 408 will tend to causedeflections 6 o that deflect radially outward in response to the radialoutward force FRO. As the wall segment 408 deflects radially outward,the overlap between the threads 406 and 408 at the interfaces 422 isreduced, thereby weakening the coupling between the set screw 404 andthe wall segment 408. The tighter the draw on the set screw 404, thegreater the radial outward force FRO and the greater the deflection ofthe wall segment 408, further decreasing the overlap at the interfaces422. Accordingly, as the torque requirements of the conventional setscrew 404 are increased, the coupling between the set screw 404 and thewall segment 408 becomes more tenuous. Over time, creep stresses maycause the deflection of the wall segment 408 and the attendant decreasein the overlap at the interfaces 422, causing the clamping force FC toreduce. This can cause loosening of the assembly and slippage of theresident spinal rod within the spinal rod receptacle 410. In someinstances, torque requirements can cause the set screw 404 to slipwithin the spinal rod receptacle 410 during implantation.

A threaded arrangement utilizing threads having the canted cantileverprofile arrangement 450 is depicted at FIGS. 26 and 26A. The variousthreads 94, 96, 126, 154, 156, and 268 (FIGS. 2, 4, and 5) of theextensible spinal support system 20 may utilize a canted cantileverprofile arrangement.

The canted cantilever profile arrangement 450, schematically depicted atFIGS. 26 and 26A, may include, for example, exterior threads 452 of aset screw 454 that are engaged with interior threads 456 of a wallsegment 458 of a spinal rod receptacle 460 (akin to opposed wallsegments 90 and 150 of the rod receptacles 24 and 34 of the extensiblespinal support system 20). Both the set screw 454 and the wall segment458 are concentric about a central axis 462 that defines the z-axis of aright-cylindrical coordinate system 464 having an axial coordinate z anda radial coordinate r. When the set screw 454 is tightened a firstdirection 466 to set against a spinal support rod 465, the clampingforce vector FC is generated, for which there is the equal and oppositeforce vector FC′ in a second direction 468 that is opposite the firstdirection 466. The force vector FC′ in turn generates reaction forcevectors FR generated at contact interfaces 472 between the exteriorthreads 452 of the set screw 454 and the interior threads 456 of thewall segment 458. The reaction forces FR generate an axial component FRZand radial component FRR.

However, unlike the conventional threaded arrangements 400, the contactinterfaces 472 of the canted cantilever profiles 450 are sloped radiallyinward (i.e., toward the central axis 462) in the first direction 466.By this arrangement, the radial component FRR is vectored inward, towardthe center axis 466. The forces so generated will tend to causedeflections 6 i of the wall segment 458 that is radially inward inresponse to the radial inward force FRI. Because of the radial inwarddeflections 6 i, the wall segments 458 tend to be supported by the setscrew 454. Accordingly, the coupling between the set screw 454 and thespinal rod receptacle 460 provided by the canted cantilever profilearrangement 450 is stronger and can provide a greater clamping force FCthan can the conventional threaded arrangement 400 of spinal rodreceptacle 410.

For the extensible spinal support system 20, the interior threads 94,154 of the base and extension rod receptacle 24, 34 interact with theset screws 42, 44 in the manner described attendant to the cantedcantilever profile arrangement 450 of FIGS. 26 and 26A. The exteriorthreads 96, 156 of the base and extension rod receptacle 24, 34 may alsoimplement a canted cantilever arrangement (see, e.g., FIGS. 2, 4, and5), but may be configured to generate different forces and deflections.For example, the exterior threads 96, 156 of the base and extension rodreceptacle 24, 34 are sloped radially outward (i.e., away the centralaxis 462) in the distal direction 74. By this arrangement, the radialcomponents of the reaction forces at the interface of the exteriorthreads 96, 156 and the interior threads 126, 226 of the skirt portions124, 224 is vectored outward, away from the center axis 67. The forcesso generated will tend to cause splaying of the rod receptacle 24, 34,i.e., to cause the wall segments 90, 150 to deflect radially outward.Because of the radial outward deflections, the wall segments 90, 150tend to be supported by the skirt portions 124, 224. The skirt portions124, 224, being tangentially continuous, incurs a hoop stress thatfurther counters the outward radial forces and limits splaying. Theoutward radial forces at the exterior threads 96, 156 also tend tocounter and can be tailored to balance the inward radial forces FRI tofurther reduce overall radial deflection (splaying) and deformation ofthe wall segments 90, 150.

Alternatively, the exterior threads 96, 156 of the receptacles 24, 34and the interior threads 126, 226 of the skirt portions 124, 224 may beof a conventional arrangement. Conventional threads, as describedattendant to FIGS. 25 and 25A, provide radial outward forces that aresubsequently supported by the skirt portions 124, 224 and as a counterto the radial inward force FRI, to prevent splaying.

Each of the additional figures and methods disclosed herein can be usedseparately, or in conjunction with other features and methods, toprovide improved devices and methods for making and using the same.Therefore, combinations of features and methods disclosed herein may notbe necessary to practice the disclosure in its broadest sense and areinstead disclosed merely to particularly describe representative andpreferred embodiments.

Various modifications to the embodiments may be apparent to one of skillin the art upon reading this disclosure. For example, persons ofordinary skill in the relevant arts will recognize that the variousfeatures described for the different embodiments can be suitablycombined, un-combined, and re-combined with other features, alone, or indifferent combinations. Likewise, the various features described aboveshould all be regarded as example embodiments, rather than limitationsto the scope or spirit of the disclosure.

Persons of ordinary skill in the relevant arts will recognize thatvarious embodiments can comprise fewer features than illustrated in anyindividual embodiment described above. The embodiments described hereinare not meant to be an exhaustive presentation of the ways in which thevarious features may be combined. Accordingly, the embodiments are notmutually exclusive combinations of features; rather, the claims cancomprise a combination of different individual features selected fromdifferent individual embodiments, as understood by persons of ordinaryskill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

Unless indicated otherwise, references to “embodiment(s)”, “disclosure”,“present disclosure”, “embodiment(s) of the disclosure”, “disclosedembodiment(s)”, and the like contained herein refer to the specification(text, including the claims, and figures) of this patent applicationthat are not admitted prior art.

For purposes of interpreting the claims, it is expressly intended thatthe provisions of 35 U.S.C. 112(f) are not to be invoked unless thespecific terms “means for” or “step for” are recited in the respectiveclaim.

What is claimed is:
 1. A spinal support system, comprising: a first rodreceptacle for mounting to a pedicle screw, said first rod receptaclehaving a first side wall that includes a first interior surface and afirst exterior surface, said first side wall defining a first pair ofdiametrically opposed slots that extend axially along said first sidewall and are open at a proximal end of said first rod receptacle, saidfirst interior surface defining first interior threads, said firstexterior surface defining first exterior threads; and an extensionassembly including a second rod receptacle mounted to a base portion,said second rod receptacle including an internal flange having aninterior face and defining an axial thickness, said base portionincluding a mounting platform and a skirt portion that extends from saidmounting platform, said skirt portion including interior threads formating with said first exterior threads of said first rod receptacle,said second rod receptacle having a second side wall that includes asecond interior surface and a second exterior surface, said second sidewall defining a second pair of diametrically opposed slots that extendaxially along said second side wall and are open at a proximal end ofsaid second rod receptacle, said second interior surface defining secondinterior threads, wherein said extension assembly includes a pivotmember that attaches said second rod receptacle to said base portion,said pivot member including a head portion and a shaft portion, saidshaft portion including a stop that cooperates with said base portion todefine a predetermined axial gap dimension between said head portion andsaid mounting platform of said base portion, said shaft portion being infixed relationship with said mounting platform, said head portion ofsaid pivot member being dimensioned to extend over said interior face ofsaid internal flange to couple said second rod receptacle and said baseportion, said axial gap being greater than said axial thickness of saidinternal flange to enable monoaxial rotation of said extension rodreceptacle about said pivot head portion.
 2. The spinal support systemof claim 1, wherein: said second rod receptacle defines an opening at adistal end thereof, said opening sized to accommodate passage of saidshaft portion of said pivot member; and said mounting platform of saidbase portion defines a center hole for receiving said pivot member. 3.The spinal support system of claim 2, wherein said shaft portionincludes external shaft threads formed on an exterior surface thereof,and said center hole includes interior threads for mating with saidexternal shaft threads.
 4. The spinal support system of claim 2, whereinsaid shaft portion is right cylindrical and includes a smooth exteriorsurface, and said center hole is right cylindrical and dimensioned for asliding fit with said shaft portion.
 5. The spinal support system ofclaim 2, wherein said shaft portion is welded to said base portion. 6.The spinal support system of claim 2, wherein said shaft portion isswaged to said base portion.
 7. The spinal support system of claim 1,wherein: said head portion of said pivot member is one of a flat headand a countersink head; and said interior face of said internal flangeof said second rod receptacle is machined to conform to said headportion to enable selective monoaxial rotation about said head portion.8. The spinal support system of claim 1, wherein a set screw portion isintegral with and extends from a distal face of said mounting platform,said set screw portion including threads configured to mate with saidfirst interior threads of said first rod receptacle.
 9. The spinalsupport system of claim 8, wherein said threads of said set screwportion and said first interior threads of said first rod receptacledefine canted cantilever profiles configured to threadably engage eachother.
 10. The spinal support system of claim 1, wherein said secondexterior surface of said second rod receptacle includes second exteriorthreads.
 11. The spinal support system of claim 10, comprising a capincluding a skirt portion having interior threads for mating with saidsecond exterior threads of said second rod receptacle.
 12. The spinalsupport system of claim 1, wherein said first exterior threads and saidinterior threads of said skirt portion define canted cantilever profilesconfigured to threadably engage each other.
 13. A spinal rod supportsystem, comprising: an extension rod receptacle including an internalflange at a distal end, said internal flange defining an axialthickness; a base portion including a mounting platform that defines acenter hole accessible from a proximal face of said mounting platform; apivot member including a head portion and a stop, said stop registeringagainst said proximal face of said platform to define a predeterminedaxial gap dimension between said head portion and said mounting platformthat is greater than said axial thickness of said internal flange ofsaid extension rod receptacle; and means for coupling said pivot memberto said base portion, wherein said internal flange of said extension rodreceptacle is captured between said head of said pivot member and saidproximal face of said mounting platform, said extension rod receptaclebeing monoaxially rotatable about said head portion.
 14. The spinalsupport system of claim 13, wherein said means for coupling saidextension rod receptacle to said base portion includes said pivot memberthreadably engaged with said center hole.
 15. The spinal support systemof claim 13, wherein said means for coupling said extension rodreceptacle to said base portion includes said pivot member swaged tosaid center hole.
 16. The spinal support system of claim 13, whereinsaid means for coupling said extension rod receptacle to said baseportion includes said pivot member fused to said center hole.
 17. Thespinal support system of claim 16, wherein said pivot member is weldedto a periphery of said center hole at a distal face of said baseportion.
 18. The spinal support system of claim 13, comprising: a baserod receptacle; and means for coupling said base portion to said baserod receptacle.
 19. The spinal support system of claim 18, wherein: saidbase portion includes a skirt portion; and said means for coupling saidbase portion to said base rod receptacle includes threaded engagement ofsaid skirt portion to said base rod receptacle.
 20. The spinal supportsystem of claim 19, wherein: said base portion includes a set screwportion that is unitary with and extends from a distal face of saidmounting platform; and said means for coupling said base portion to saidbase rod receptacle includes threaded engagement of said set screwportion to said base rod receptacle.